The present invention relates to a method for forming a coating film by ion plating on a substrate surface or, more particularly, to a method for forming a decorative coating of blackish color tone by ion plating on the surface of a metallic substrate such as watch cases, watch straps, bracelets, rings and the like used for personal ornament.
As a trend in recent years, various goods for personal ornament use such as watch cases are required to be imparted with a color of specific hue and tone full of high-class sense instead of the traditional golden or silvery metallic luster. In accordance with such a strong demand, various methods have been developed and practiced for the surface finishing of a metallic substrate including the methods of colored plating, dyeing, coating and the like. These prior art methods are not quite satisfactory in one or more of disadvantages and defects that the desired high-class sense cannot be obtained, that the surface finished by the method has no sufficient durability due to the poor corrosion resistance and susceptibility to discoloration, peeling of the surface layer and scratches and the like mechanical damages, that the process of the method is complicated and troublesome and that the process uses or discharges some noxious chemicals and gase to cause serious problems in connection with the worker's health and environmental pollution.